The present invention relates to a novel photo-catalyst. Especially, the present invention relates to a photo-catalyst comprising RuO2-loaded A2XnOm or RuO2-loaded BXnOm (wherein A is an alkali metal atom, B is an alkali earth metal atom or Zn, X is a metallic ion with d10 configuration, n=m/2 or n=m/3 and n is 2), more especially relates to a photo-catalyst used for complete decomposition of water.
The photo decomposition reaction of water is broadly interested from the view point of photo energy transformation. While, a photo-catalyst which shows activity to the photo decomposition reaction of water can be considered to be a high quality photo functional material possessing functions such as photo absorption, electric charge separation or surface oxidation-reduction reaction.
Kudo, Kato et al are explaining that alkali tantalate or alkali earth elements are the photo-catalyst showing high activity to the complete photo decomposition reaction of water by quoting various prior arts [Catal. Lett., 58(1999). 153-155, Chem. Lett., (1999), 1207, Surface Vol.36, No.12(1998), 625-645 (shortened to document A)].
In above mentioned document A, there is an explanation about an useful photo-catalyst materials for proceeding the decomposition reaction of water to hydrogen and oxygen using a photo-catalyst, and many indications about photo-catalyst used for complete photo decomposition reaction of water are mentioned.
In the document, it is reported that the authors has first at all found, that tantalate acts as a photo-catalyst which generates oxygen and hydrogen from pure water according to stoichiometric ratio without a promoter, and then has found that the catalyst activity is remarkably improved by carrying NiO promoter (right column of 635th page).
Further, there is an explanation reporting that also K4Nb6O17 can generate oxygen and hydrogen from pure water without a promoter, and the fine crystalline of it obtained by pulverizing it indicates remarkably high activity. Furthermore, there is an illustration that a compound having perovskite structure such as K2La2Ti3O10 has excellent photo-catalyst activity, because the hydration reaction can easily occur between layers.
In FIG. 6 of 629th page, there is an explanation about main elements composing of un-uniform type photo-catalyst materials, and in which there is a description explaining that the oxide composed of a transition metal ion possessing d0 and d10 electron arrangement or a metal ion of p-block. And, in 640th page, following explanations are described. Namely, the band gap of In2O3(ZnO)m composed of laminated structure of In2O and ZnO3 is smaller than that of In2O3 or ZnO alone, and generates hydrogen by photo decomposition of methanol aqueous solution under the visible radiation or generates oxygen by photo decomposition of AgNO3 aqueous solution under the visible radiation. Further, regarding to xcex2-Ga2O3, there is also following explanation. Namely, by forming a solid solution with In2O3, the band gap of it becomes smaller maintaining the structure of xcex2-Ga2O3, and can generate hydrogen and oxygen by photo decomposition of water under the presence of methanol or AgNO3 which are a sacrificial reagent, but not extends to the responsibility for visible radiation. However, there is no explanation teaching activity in regard to water decomposition reaction or Sb.
Concerning above mentioned circumstances, the inventors of the present invention have carried out intensive study to make the photo-catalyst which uses a transition metal ion possessing d10 electron arrangement generate high activity, especially have repeatedly continued various experiments in regard to various compounds aiming to provide a catalyst which make enable the photo decomposition of water.
From the results conduced by these experiments, the inventors of the present invention have found the following fact and have accomplished the present invention. That is, the salt of alkali metal or alkali earth metal and transition metal ion possessing d10 electron arrangement can act as a catalyst which make enable the complete photo decomposition of water by loading RuO2, without the presence of methanol or AgNO3 which are a sacrificial reagent used in above mentioned prior arts.
The present invention is the photo-catalyst comprising RuO2-loaded A2XnOm or RuO2-loaded BXnOm (wherein A is an alkali metal atom, B is an alkali earth metal atom or Zn, X is a metal ion with d10 configuration, n=m/2 or n=m/3 and n is 2). Desirably, A2XnOm or BXnOm (wherein A is an alkali metal atom, B is an alkali earth metal atom or Zn, X is a metal ion with d10 configuration, n=m/2 or n=m/3 and n is 2) is the photo-catalyst obtained by a coprecipitation powder calcination method calcined at the temperature of 1150 to 1200xc2x0 C., more desirably, X is In, Ga or Sb, an alkali metal atom is Na, K or Rb and an alkali earth metal atom is Ca, Sr or Ba.
The second important point of the present invention is the photo-catalyst for photo decomposition reaction of water comprising RuO2-loaded A2XnOm or RuO2-loaded BXnOm (wherein A is an alkali metal atom, B is an alkali earth metal atom or Zn, X is a metal ion with d10 configuration, n=m/2 or n=m/3 and n is 2).